Combine water and rice, cover, and microwave on HIGH for 10 minutes. Continue cooking during meat preparation or until liquid is absorbed and rice is tender.
In a microwave-safe bowl, combine meat with oil and toss to evenly coat. Cover and microwave on HIGH for 5 minutes.
Remove meat from bowl and set aside. Add mushrooms and onion. Cover and microwave until mushrooms are tender, about 5 minutes.
Combine water and flour; stir into mushroom mixture. Sprinkle with dry mustard, salt and pepper. Microwave, uncovered, to boiling, about 30 seconds; then microwave until thick, about 1 minute.
Stir in meat, then sour cream. Microwave, uncovered, until hot, about 1 minute. Serve over rice.Servings: 4